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Biomechanics & Rehabilitation > Biomechanics of Soft Tissue > Flashcards

Biomechanics of Soft Tissue Flashcards

1
Q

What is the tendon composition?

A 
70% water
30% ➡️ 70-90% Type 1 Collagen
              10-15% Cells
              2-5% Proteoglycans
              0.5-5% Other Glycoproteins
              0.5-3% Elastin
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2
Q

What is the structure of a tendon?

A

It is a fibre composite material
➡️ multiple hierarchical levels of collagen
➡️ Proteoglycanous matrix binding
➡️ Interspersed with cells (tenocytes)

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3
Q

What can cause a change in the tissue cells?

A

Mechanical stimuli

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4
Q

What is the cellular response mechanical stimuli causes in tissue cells?

A

Proliferation
Matrix synthesis
Matrix degradation
Cell/matrix orientation

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5
Q

In terms of tendons, what is homeostasis?

A

Normal tissue turnover

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6
Q

In terms of tendons, what is disease/degeneration?

A

Tissue degradation

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7
Q

In terms of tendons, what is tissue repair?

A

Tissue anabolism and regeneration

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8
Q

What are the properties of an Energy Storing tendon? (6)

A

Eg Human Achilles, Equine SDFT

  • high strains
  • elastic recoil in use
  • high incidence of tendinopathy
  • less stiff
  • highly fatigue resistant
  • less viscoelastic
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9
Q

What are the properties of Positional tendons? (6)

A

Eg human anterior tibialis, equine CDET

  • low strains
  • less elastic
  • efficient strain transfer from muscle to bone
  • more stiff
  • less fatigue resistant
  • more viscoelastic
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10
Q

What happens when strain is applied to energy storing tendons?

A

➡️ fibre sliding

  • significantly more fibre sliding in extensor tendons
  • significantly better recovery from loading in energy storing flexor fascicles
  • significantly less hysteresis (better recovery) in energy storing flexor fascicles
  • extension = sample rotation
  • good recovery & elasticity
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11
Q

What happens when strain is applied to a positional tendon?

A

➡️ rotation of fibres

  • significantly more fascicle rotation in flexor tendons
  • extension = fibre sliding
  • poor recovery and less elastic
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12
Q

What happens in aging and energy storing tendons?

A
  • The tightness of the helix reduces with age
  • the recoverability of the helix reduces with age
  • the capacity for fascicle sliding reduces with age
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13
Q

What is the function of a tendon?

A

It transmits muscle forces to the skeleton
- provides a link from compliant muscle to stiff bone
- acts as a lever arm which reduces the need for large muscles
- reduces the need to have muscles near joints
- efficiently transfers forces
▶️▶️ limited extensibility
▶️▶️ some protection from impact loading
▶️▶️ can store energy to assist in locomotion

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14
Q

When is tendinopathy not tendinitis?

A

If it is chronic

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15
Q

What is the pathological process of tendinopathy?

A

LOAD - causing balanced tenocyte catabolism/anabolism
⬇️overload
A REACTIVE tendon
⬇️ tenocyte mediated disease process, failed healing
A DEGENERATIVE tendon

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16
Q

Tenon loading in younger people with tendinopathy

A 
Reasonable strength
High load demands
Isometrics, eccentrics, concentric a
Power
Endurance➡️load➡️speed
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17
Q

Tendon loading in middle age recreational athletes with tendinopathy

A 
Reasonable strength
Lower load demands
Isometrics, eccentrics, concentrics
Power
Endurance➡️load➡️speed
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18
Q

Tendon loading in older or sedentary patients with tendinopathy

A

Weak - intrinsic factors of adiposity or menopause
Isometrics, eccentrics, concentrics
Endurance➡️load➡️speed

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19
Q

Define Hooke’s Law

A

An increase in stress causes a proportional increase in strain

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20
Q

Define Youngs Modulus

A

The ratio of stress to strain

21
Q

Define the elastic range

A

The range in which something can be stretched, where when released it will return to its original shape

22
Q

Define the plastic range of something

A

The range in which as a force is applied the shape is deforming permanently

23
Q

Define poisons ratio

A

The ratio of the proportional decrease in a lateral measurement to the proportional increase in length in a sample which is elastic ally stretched

24
Q

Define generalised Hooke’s Law

A

Strain can exist without stress

25
Q

Which type of collagen is most common in connective tendons and ligaments?

A

Type 1

26
Q

How is collagen organised and why?

A

Organised structurally to allow both tensile stiffness and strength to tissue

27
Q

What is the structure of the basic unit of collagen?

A

Tropocollagen to collagen triple helix

  • 3 peptide alpha chains
  • peptide chains packed together by hydrogen bonds
  • tropocollagens covalently bonded to other neighbouring tropocollagens to form staggered D-periods
  • microfibrils➡️subfibrils➡️collagen fibrils
28
Q

What is the ligament structure?

And what is the function of this structure

A

75-80% dry weight = type 1 collagen
55-65% wet weight = water

Thought to provide lubrication
Influences viscoelastic

29
Q

What are the function of tendons

A
  • Connects muscle to bone - force transmission between the 2 structures
  • vary in size and shape in the body
    • can pass through bony features
  • -specialised connective tissue sheaths guide tendon across joints to maintain correct orientation and force transduction
30
Q

What is the primary function of a tendon?

A

Transmit muscle force

31
Q

What is the difference between tendons and ligaments?

A
  • Collagen fibres in tendon tend to be aligned in tendon compared to ligaments
  • fewer fibroblasts than in ligaments
32
Q

What are the stages in muscle contraction?

A
  1. Myosin head attaches to the actin myofilament, forming a cross bridge
  2. Inorganic phosphate generated in the previous contraction cycle is released, initiating the power stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it towards the M line. Then ADP is released
  3. As the new ATP attaches to the myosin head, the link between myosin and actin weakens and the cross bridge detaches
  4. As ATP is split into ADP and Inorganic phosphate, the myosin head is energised (cocking into the high energy confirmation)
33
Q

Define the motor unit

A

Single motor neurone and the muscle fibres it innervates

- hamstrings 300:1 muscle/nerve ratio

34
Q

What is the size principle of motor unit recruitment?

A
  • Orderly hierarchy of motor unit recruitment based on size
  • Low levels of force; small (low force) motor unit with thin axons and small, easily excitable motor unit are recruited
  • As force requirements increases, systematic recruitment of larger motor unit
35
Q

What are the biochemical properties of muscle fibres?

A

Oxidative capacity

Type of ATPase

36
Q

What are the contractile properties of muscle fibres?

A

Maximal force production
Speed of contraction
Muscle fibre efficiency (mechanical work: metabolic cost)

37
Q

What is the difference between contraction in Type 1, type 2a and 2b fibres?

A

Type 1 contraction slow
Type 2a contraction medium
Type 2b contraction fast

38
Q

What is the difference between size of motor neuron in Type 1, type 2a and 2b fibres?

A

Type 1: small
Type 2a: medium
Type 2b: very large

39
Q

What is the difference between resistance to fatigue in Type 1, type 2a and 2b fibres?

A

Type 1: high
Type 2a: fairly high
Type 2b: low

40
Q

What is the difference between activity the fibre is used for in Type 1, type 2a and 2b fibres?

A

Type 1: aerobic
Type 2a: long term anaerobic
Type 2b: short term anaerobic

41
Q

What is the difference between maximum duration of use in Type 1, type 2a and 2b fibres?

A

Type 1: hours

Type 2a:

42
Q

What is the difference between power of contraction in Type 1, type 2a and 2b fibres?

A

Type 1: low
Type 2a: medium
Type 2b: very high

43
Q

What is the difference between major fuel storage in Type 1, type 2a and 2b fibres?

A

Type 1: triglycerides

Type 2a&b: creatine phosphate and glycogen

44
Q

In hills three-element muscle model, define the active force of the contractile element

A

The active force comes from the force generated by the actin and myosin crossbridges at the sarcomere level

45
Q

In hills three-element muscle model, define the three elements

A

Contractile element-
Force generation from sarcomere from crossbridge formation
2 nonlinear springs-
- parallel element (passive force of when endomysium when stretched)
- series element (tendon and intrinsic elasticity of myofilaments)

46
Q

What happens to the force of the muscle when the sarcomeres lengthen?

Why?

A

Active force decreases
Passive force increases

The rate of detachment of actin myosin crossbridge sits slower during sarcomere lengthening so there is a greater force

47
Q

What is the force generated during muscle contraction?

A

The force per unit area generated by muscle fibres by cross-sectional area

48
Q

What is the difference in force generated between bipennate and parallel arrangement muscles?

A
  • force generated by bipennate can be much larger
  • bipennate muscles do not expand laterally on contraction
  • bipennate muscles shorten more slowly then parallel
49
Q

What is the force-velocity relationship for muscle tissue?

A
  • When the resistance (force) is negligible, muscle contracts with maximal velocity
  • as the load progressively increases, concentric contraction velocity slows to zero at isometric maximum contraction
  • as the load increases further, the muscle lengthens eccentrically

Biomechanics & Rehabilitation (10 decks)

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